I believe Whelen introduced Y-249 (Yelp 249) as an option to specify a third siren tone that's compliant with California Title 13 regulations. Remember, it's not just the tone restriction to Wail and Yelp, T13 actually specifies the technical aspects of each tone. For a time period, one could order a Whelen siren with Wail, Yelp and Y-249 in order to have a T13-compliant package, whereas previously it was restricted to Wail and Yelp only.
Alternate Wail and Alternate Yelp, which are Whelen's version of the Unitrol tones, were introduced later. I believe they too are compliant for use in California. Regarding Simulated Mechanical, I believe that is NOT compliant for use in California; but I do not have confirmation of that.